1. Field of the Invention
The present invention relates to a method and device for measurement of a viscosity of liquids and, more particularly, a method and device applicable to measurement of the viscosity of bloods.
2. Description of Related Art
It is well-known that the health conditions of a person influence the viscosity of bloods. In fact, the viscosity of a blood of a person who suffers from anemia, chronic renal insufficiency requiring hemodialysis, myocardial infarction, diabetes mellitus or malignant tumor, differs greatly from that of a person in normal health. In advanced nations, with an increase in the average age of the population, adult diseases such as, for example, myocardial infarction, thrombo-embolism and diabetes mellitus are gradually increasing. Thus, the measurement of the viscosity of bloods is an important and effective factor essential for therapy and/or prevention of diseases.
As is known, the blood is non-Newtonian in its flow characteristics, whereas the blood plasma behaves Newtonian. It is said, therefore, that the non-Newtonian behaviors of the blood result from the presence of blood corpuscles suspended in the blood plasma. In particular, it is said that factors which influence the flow characteristics of the blood are the orientation of blood corpuscles and their various shapes including disc shapes with concave surfaces, streamlined shapes or projectile shapes. The effect of such factors on the flow characteristics varies with a period of time elapsed from the blood collecting, and is affected by addition of other substances such as, for example, anticoagulants to the blood. Thus, the best way to determine the flow characteristics of blood including its non-Newtonian behaviors is to choose the blood running in the body as the object of the measurement.
However, there is no viscometry which makes it possible to directly measure the flow characteristics of the blood running in the body. To this end, it is inevitable to use collected blood as the object of measurement. It is therefore required to measure the flow characteristics of the blood correctly in the least time possible after blood-collecting, as well as to collect the blood without incorporating any other materials such as anticoagulants into the blood.
In addition, in order to adapt rheological blood tests to a routine clinical medicine, it is required to satisfy the following three conditions: (a) the measurement can be made with the natural blood; (b) the measurement can be made instantly at the bed side; and (c) the viscometer is easy to operate and operable for any person.
So far, various devices have been developed to measure the viscosity of liquids or solutions. In the sphere of clinical medicine, however, there have been employed two devices, i.e., a capillary viscometer and a rotation viscometer. In the former, the viscosity of a liquid is measured by introducing the liquid into the capillary viscometer, and then causing the liquid to flow under external forces such as the gravitational force through a capillary or a fine tube of uniform bore to obtain the time required for its meniscus to pass through between predetermined levels. The measurement is carried out several times at various flow rates and under pressure heads resulting from a length of the capillary. Such a capillary viscometer has been used widely to measure the viscosity of blood plasma. However, it is rarely the case that the capillary viscometers are applied to measure the viscosity of blood as the natural blood is non-Newtonian in its flow characteristics.
The measurement of the viscosity of bloods has generally been carried out with rotation viscometers. A typical rotation viscometer comprises two concentric cylinders, the inner or outer cylinder being rotated in or rotated around the fixed outer or inner cylinder. In such a viscometer, the liquid is placed between two cylinders and either of the cylinders is rotated around its axis to measure its torque.
However, the rotation viscometers have the following disadvantages: (a) several measurements must be made on the same blood at different shear stresses; (b) calculations are troublesome and lead to noticeable errors as they require graphical differentiation of logarithmic values; (c) special and unstable flows such as Taylor vortex takes place at high rotating rates; (d) the liquid to be examined generates heat by its viscosity; (e) there is a fear of causing deflection of blood corpuscles by means of the centrifugal force; (f) the measurement for each specimen takes a long time; and (g) the viscometer is troublesome to handle as the viscometer must be cleaned after every measurement by washing it with water and then drying the same to remove the blood adhered thereto.
To solve these problems, various new methods employing a roller pump system or a hollow fiber module have been proposed to measure the viscosity of bloods. However, none of the viscometers of the prior art satisfies all the conditions required for application to the clinical medicine.